Marine and Offshore Technology Center India Blog

  Ship Structural Failure Modes Cracks can occur due to fatigue and brittle fracture. Buckling is due to in plane compressive stresses during hogging and sagging of the ships. An Indent occurs during cargo handling. Any dent in the plate due to lateral hitting of the ship by external vessels like tugs is in Indent. Corrosion is one of the main failure modes that presents always in the maritime field. 1.        CRACKS: Most of the cracks that occur in ship are due to fatigue. Fatigue is the failure of a material by cyclic loading. A large number of complicated welded plate joints can be found in an ocean- going ship. During the service time of the vessel these plates are exposed to time-varying loads caused by the irregular seaway, the propulsion system, and changes in the loading conditions. Hard spots, such as connections between longitudinal stiffeners and web frames, where local rises in stress intensity can be found, may therefore be prone to f...

  2 stroke engine and 4 stroke engine vibration characteristics Two-stroke engines typically have a higher vibration frequency than four-stroke engines due to their simpler design and the fact that the power stroke occurs twice as often in a two-stroke engine for every revolution of the crankshaft. This can lead to a rougher or more "buzzy" feeling when operating a two-stroke engine. On the other hand, four-stroke engines have a lower vibration frequency because the power stroke only occurs once every two revolutions of the crankshaft, which can result in a smoother operation. Additionally, four-stroke engines are typically more complex in design with additional components such as valves and camshafts which can help dampen engine vibrations. In addition to the vibration frequency, the magnitude of the vibration is also different between two-stroke and four-stroke engines. Two-stroke engines often have a higher amplitude of vibration because they have fewer components to absor...

How ship float on water?  

 Trend's in Marine Engineering Emphasis on sustainability and environmental protection: There has been a trend towards the development of more efficient and environmentally friendly marine vehicles, such as electric and hybrid propulsion systems, and the use of alternative fuels like biofuels and LNG. Advancements in materials and technologies: There has been a focus on the use of advanced materials and technologies to improve the safety, reliability, and performance of marine systems. Growth of offshore renewable energy: The development of offshore renewable energy generation, such as wind and wave power, has led to the growth of specialized marine engineering technologies and systems for the construction and maintenance of offshore energy facilities. Increased automation and digitalization: There has been a trend towards the increased automation and digitalization of marine systems, including the use of sensors, data analytics, and autonomous systems to improve efficiency and ...

  Superelement:   1. What is superelement and why it is used in FEA? : A superelement is a reduced representation of a structure. 2 .  Why it is used:  :  To reduce the solution time of solver without affecting accuracy 3. Types of superelement? a.Static condensation superelement - This method reduces the elastic FE model and load  vectors (e.g., points and pressure) to the interface degrees of freedom b. Dynamic reduction superelement - This method reduces the elastic FE model to the interface degrees of freedom and a set of normal modes, which are generated from static modes and  normal modes analyses. c. Component dynamic superelement - This method is efficient for models under iterative  loading

  Finite Element Mesh Quality Parameter: ·          Aspect Ratio :  The element aspect ratio in a 2D element or a face of a 3D element is the ratio between the longest and shortest element dimensions ·          Skewness: s kewing is defined as the deviation of vertex angles ( 𝛽 ) from 90° for quadrilateral shaped elements, and from 60° for triangularly shaped elements. ·          Warpage: When element nodes are not in the same plane, the element is warped. ·          Max / Min length : Maximum and minimum dimension of the element ·          Max / Min Angle Quadrilateral / Triangular : Individual maximum and minimum angles of the element. ·          Jacobian Ratio - A scale factor to describe the transformation of the coordi...

  Fatigue Analysis Procedure: Fatigue Analysis      About 90% of service failures are caused by fatigue that leads to a fracture, and sometimes the     failure locations predicted from the static or dynamic analysis are different from the test and field      observations . One of the reasons for this is that the failure is caused by fatigue damage.         

  ·           Loads needs to be considered during ship structure analysis: 1. Hull Girder Loads   consist of wave-induced and still water loads on the hull girder. This load should be considered for longitudinal structure in the main hull, and for the interaction of a long continuous deckhouse (superstructure). 2. Hydrostatic Loads are pressure loads due to fluids. The pressure could be either internal or external. Examples of hydrostatic loads are external pressure of the bottom and sides of shell plating, and internal pressure in tanks and on watertight bulkheads. 3. Hydrodynamic Loads consist of liquid sloshing in tanks, shipping of green water on the weather deck and impacting on the house front, and wave slap on all exposed structure and equipment above the waterline, etc. 4. Live Loads consist of uniform deck loading, concentrated loads such as forklift or aircraft landing and parking loads, support reactions from stanchio...

  Finite Element Analysis Boundary Condition for Simulating Symmetry:   Many structures have one or more planes of symmetry. It is possible to take advantage of this in FEA, and model just one portion of the structure. Through various devices it is possible to analyze structures with a plane of symmetry but subject to non-symmetric loads. Such approaches are used to reduce modelling and computational effort. In engineering applications, the most commonly encountered types of symmetry are reflective symmetry, rotational symmetry and inversion symmetry as shown in Figure In engineering problems the characterization of symmetry requires not only geometrical symmetry, but also symmetry with respect to material properties and restraints. When only part of a symmetric structure is modelled, the symmetric or anti symmetric boundary conditions must be applied at artificial boundaries introduced because of symmetry. If the y-z plane is the plane of symmetry, and Ux, Uy...